In tube-and-sheet heat exchangers, for example those used in a nuclear steam generator, problems are encountered in the form of tubes which become defective or damaged. These tubes are generally effectively removed from operation by plugging both ends of the tubes during a maintenance shutdown and continuing the operation of the steam generator with only the remaining tubes in operation. One means used in the past for plugging the tubes was by welding a plug into each of the tube ends, as disclosed in U.S. Pat. No. 4,262,187, which issued on Apr. 14, 1981.
This works fine until a point is reached where there are so many tubes plugged that there is insufficient capacity left for continued practical operation of the steam generator. Then the unit is normally taken out of operation altogether and replaced with an entire new steam generator. Since the cost of replacing an entire steam generator is extremely high, other means of handling the situation is presently being considered. One means is to plug the tubes by means of plugs which can be readily and easily removed at a later time. Thus when too many tubes have been removed from operation, the unit can be shut down, the plugs can be removed, and the tubes can be thoroughly inspected and tested to see which tubes can be effectively repaired, for example by sleeving. If enough tubes can be repaired, the useful life of the steam generator can be greatly extended.